Action Potential (session 5)

Question 1

What does the action potential depend on?

Answer 1

Ionic gradients

Relative permeability of the membrane

Question 2

What is the action potential?

Answer 2

Change in voltage across the membrane

Question 3

True or false: the action potential is propagated with loss of amplitude

Answer 3

FALSE - there is no loss of amplitude

Question 4

True or false: depolarisation to threshold initiates an action potential at the axon hillock

Answer 4

TRUE

Question 5

What is the driving force?

Answer 5

Difference between membrane potential and equilibrium potential

Question 6

Complete the sentence:

If the conductance (g) to any ion is increased, the membrane potential (Vm) will move ______ to the equilibrium potential for that ion.

Answer 6

Closer

Question 7

What is the conductance of the membrane to a particular ion dependent on?

Answer 7

The number of channels for that ion that are open

Question 8

True or false: sodium equilibrium potential dictates the generation of an action potential

Answer 8

TRUE

Question 9

True or false: not many ions need to flow for an AP to be initiated

Answer 9

TRUE

Question 10

What is capacitance?

Answer 10

Ability to store charge

Question 11

True or false: the Na+/K+ ATPase pump is needed for repolarisation

Answer 11

FALSE

Question 12

What do voltage-clamps allow?

Answer 12

Membrane currents to be measured at a set membrane potential

Question 13

What is the absolute refractory period?

Answer 13

Nearly all Na+ channels are in their inactivated state and no matter how strong the stimulus is, no AP is initiated

Question 14

What is the relative refractory period?

Answer 14

Na+ channels are recovering from inactivation, excitability returns towards normal as number of channels in the inactivated state decreases. If there is a strong stimulus, another AP may be initiated

Question 15

How many alpha subunits does the functional channel of a voltage gated Na+ channel have?

Answer 15

One

Question 16

How many alpha subunits does the functional channel of a voltage gated K+ channel have?

Answer 16

Four

Question 17

True or false: voltage gated K+ channel is 1/4 the size of a Na+ channel

Answer 17

TRUE - 4 subunits are needed to make a functional K+ channel

Question 18

True or false: channels open and close in a random manner

Answer 18

TRUE

Question 19

How do local anaesthetics work?

Answer 19

By blocking Na+ channels (no AP)

Question 20

Give an example of a local anaesthetic

Answer 20

Procaine

Question 21

In what order do local anaesthetics block axons?

Answer 21

1. Small myelinated axons
2. Unmyelinated axons
3. Large myelinated axons

Question 22

Complete the sentence:

Injection of current into an axon will cause the resulting charge to spread along the axon and cause an _________ _____ ______ in the membrane potential.

Answer 22

Immediate local change

Question 23

What does membrane resistance depend on?

Answer 23

Number of ion channels open

Question 24

Complete the sentence:

The lower the resistance, the _____ ion channels are open.

Answer 24

More

Question 25

Complete the sentence: A high capacitance leads to the voltage changing more ______ in response to current injection

Answer 25

Slowly

Question 26

Complete the sentence: High resistance leads to a change in voltage spreading ________ along the axon

Answer 26

Further

Question 27

Complete the sentence: The wider the axon, the ______ and _______ the conductance of the AP

Answer 27

Faster | Further

Question 28

Schwann cells are in which nervous system? And what is the equivalent in the other nervous system?

Answer 28

PNS | Oligodendrocytes

Question 29

Is there a high or low density of Na+ channels at the nodes of Ranvier?

Answer 29

High

Question 30

What is saltatory conduction?

Answer 30

Action potential 'jumping' from node to node, allowing a much faster conduction velocity

Question 31

True or false: AP occurs only at nodes

Answer 31

TRUE

Question 32

How does the myelin sheath improve conduction? (4)

Answer 32

1. Large increase in membrane resistance (Rm) 2. Large decrease in membrane capacitance (Cm) 3. The above increase length constant 4. Slight decrease in time constant

Question 33

Name some diseases that affect the conduction of the AP in the CNS and briefly describe which nerves they affect (2)

Answer 33

1. Multiple sclerosis - affects all CNS nerves | 2. Devic's disease - optic and spinal cord nerves only

Question 34

Which diseases affect the conduction of APs in the PNS? (2)

Answer 34

1. Landry-Guillain-Barre syndrome | 2. Charcot-Marie-Tooth disease

Question 35

Diseases affecting the conduction of the AP result from the breakdown or damage of what?

Answer 35

The myelin sheath

Question 36

Complete the sentence: In regions of demyelination, the density of the action current is reduced because of _________ and ___________ ________

Answer 36

Resistive | Capacitance shunting